Basically https://www.ghacks.net/2020/09/16/sharex-update-brings-a-smart-eraser-new-hotkeys-and-more/

Smart Eraser Annotation Tool This is a new annotation tool in ShareX's image editor. You can find it on the toolbar, the icon sits between the cursor and blur tools. Normally, when you erase something using an image editor, it leaves behind some visual elements, e.g. white/colored patches. As a workaround, it is often better to use the blur tool instead though it isn't a completely tidy option either.

ShareX smart eraser example 2

ShareX's Smart Eraser works differently, it obfuscates the content by blending it with the background. f you look at the tool closely, you'll see it has a color-picker preview. Mouse over the area you want to erase the content from, and the tool automatically picks up the background color over the pointer's position. Use it to draw a box and the color is applied to "erase" the contents. The result looks a lot cleaner and smoother than using the blur tool or white erase.

ShareX smart eraser example smudgy

ome image editors support erasing with color, but you'll need to pick the shade manually before erasing the content. That's 2 steps, and if you pick the wrong color, you'll have to start over. ShareX's smart eraser however only works well with a single solid color background, i.e., if you use it with images that have multiple hues, the result will appear to be smudgy.Screen Recorder, Image Combiner, new hotkeys and more